gcc/config/host-linux.c

   1 /* Linux host-specific hook definitions.
   2    Copyright (C) 2004-2018 Free Software Foundation, Inc.
   3
   4    This file is part of GCC.
   5
   6    GCC is free software; you can redistribute it and/or modify it
   7    under the terms of the GNU General Public License as published
   8    by the Free Software Foundation; either version 3, or (at your
   9    option) any later version.
  10
  11    GCC is distributed in the hope that it will be useful, but WITHOUT
  12    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  13    or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
  14    License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with GCC; see the file COPYING3.  If not see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #include "config.h"
  21 #include "system.h"
  22 #include "coretypes.h"
  23 #include "hosthooks.h"
  24 #include "hosthooks-def.h"
  25
  26
  27 /* Linux has a feature called exec-shield-randomize that perturbs the
  28    address of non-fixed mapped segments by a (relatively) small amount.
  29    The feature is intended to make it harder to attack the system with
  30    buffer overflow attacks, since every invocation of a program will
  31    have its libraries and data segments at slightly different addresses.
  32
  33    This feature causes us problems with PCH because it makes it that
  34    much harder to acquire a stable location at which to map our PCH
  35    data file.
  36
  37    [ The feature causes other points of non-determinism within the
  38      compiler as well, so we'd *really* like to be able to have the
  39      driver disable exec-shield-randomize for the process group, but
  40      that isn't possible at present.  ]
  41
  42    We're going to try several things:
  43
  44       * Select an architecture specific address as "likely" and see
  45         if that's free.  For our 64-bit hosts, we can easily choose
  46         an address in Never Never Land.
  47
  48       * If exec-shield-randomize is disabled, then just use the
  49         address chosen by mmap in step one.
  50
  51       * If exec-shield-randomize is enabled, then temporarily allocate
  52         32M of memory as a buffer, then allocate PCH memory, then
  53         free the buffer.  The theory here is that the perturbation is
  54         no more than 16M, and so by allocating our buffer larger than
  55         that we make it considerably more likely that the address will
  56         be free when we want to load the data back.
  57 */
  58
  59 #undef HOST_HOOKS_GT_PCH_GET_ADDRESS
  60 #define HOST_HOOKS_GT_PCH_GET_ADDRESS linux_gt_pch_get_address
  61
  62 #undef HOST_HOOKS_GT_PCH_USE_ADDRESS
  63 #define HOST_HOOKS_GT_PCH_USE_ADDRESS linux_gt_pch_use_address
  64
  65 /* For various ports, try to guess a fixed spot in the vm space
  66    that's probably free.  */
  67 #if defined(__alpha)
  68 # define TRY_EMPTY_VM_SPACE     0x10000000000
  69 #elif defined(__ia64)
  70 # define TRY_EMPTY_VM_SPACE     0x2000000100000000
  71 #elif defined(__x86_64) && defined(__LP64__)
  72 # define TRY_EMPTY_VM_SPACE     0x1000000000
  73 #elif defined(__x86_64)
  74 # define TRY_EMPTY_VM_SPACE     0x60000000
  75 #elif defined(__i386)
  76 # define TRY_EMPTY_VM_SPACE     0x60000000
  77 #elif defined(__powerpc__)
  78 # define TRY_EMPTY_VM_SPACE     0x60000000
  79 #elif defined(__s390x__)
  80 # define TRY_EMPTY_VM_SPACE     0x8000000000
  81 #elif defined(__s390__)
  82 # define TRY_EMPTY_VM_SPACE     0x60000000
  83 #elif defined(__sparc__) && defined(__LP64__)
  84 # define TRY_EMPTY_VM_SPACE     0x8000000000
  85 #elif defined(__sparc__)
  86 # define TRY_EMPTY_VM_SPACE     0x60000000
  87 #elif defined(__mc68000__)
  88 # define TRY_EMPTY_VM_SPACE     0x40000000
  89 #elif defined(__aarch64__) && defined(__ILP32__)
  90 # define TRY_EMPTY_VM_SPACE     0x60000000
  91 #elif defined(__aarch64__)
  92 # define TRY_EMPTY_VM_SPACE     0x1000000000
  93 #elif defined(__ARM_EABI__)
  94 # define TRY_EMPTY_VM_SPACE     0x60000000
  95 #elif defined(__mips__) && defined(__LP64__)
  96 # define TRY_EMPTY_VM_SPACE     0x8000000000
  97 #elif defined(__mips__)
  98 # define TRY_EMPTY_VM_SPACE     0x60000000
  99 #else
 100 # define TRY_EMPTY_VM_SPACE     0
 101 #endif
 102
 103 /* Determine a location where we might be able to reliably allocate SIZE
 104    bytes.  FD is the PCH file, though we should return with the file
 105    unmapped.  */
 106
 107 static void *
 108 linux_gt_pch_get_address (size_t size, int fd)
 109 {
 110   size_t buffer_size = 32 * 1024 * 1024;
 111   void *addr, *buffer;
 112   FILE *f;
 113   bool randomize_on;
 114
 115   addr = mmap ((void *)TRY_EMPTY_VM_SPACE, size, PROT_READ | PROT_WRITE,
 116                MAP_PRIVATE, fd, 0);
 117
 118   /* If we failed the map, that means there's *no* free space.  */
 119   if (addr == (void *) MAP_FAILED)
 120     return NULL;
 121   /* Unmap the area before returning.  */
 122   munmap (addr, size);
 123
 124   /* If we got the exact area we requested, then that's great.  */
 125   if (TRY_EMPTY_VM_SPACE && addr == (void *) TRY_EMPTY_VM_SPACE)
 126     return addr;
 127
 128   /* If we didn't, then we need to look to see if virtual address
 129      randomization is on.  That is recorded in
 130      kernel.randomize_va_space.  An older implementation used
 131      kernel.exec-shield-randomize.  */
 132   f = fopen ("/proc/sys/kernel/randomize_va_space", "r");
 133   if (f == NULL)
 134     f = fopen ("/proc/sys/kernel/exec-shield-randomize", "r");
 135   randomize_on = false;
 136   if (f != NULL)
 137     {
 138       char buf[100];
 139       size_t c;
 140
 141       c = fread (buf, 1, sizeof buf - 1, f);
 142       if (c > 0)
 143         {
 144           buf[c] = '\0';
 145           randomize_on = (atoi (buf) > 0);
 146         }
 147       fclose (f);
 148     }
 149
 150   /* If it isn't, then accept the address that mmap selected as fine.  */
 151   if (!randomize_on)
 152     return addr;
 153
 154   /* Otherwise, we need to try again with buffer space.  */
 155   buffer = mmap (0, buffer_size, PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0);
 156   addr = mmap (0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
 157   if (buffer != (void *) MAP_FAILED)
 158     munmap (buffer, buffer_size);
 159   if (addr == (void *) MAP_FAILED)
 160     return NULL;
 161   munmap (addr, size);
 162
 163   return addr;
 164 }
 165
 166 /* Map SIZE bytes of FD+OFFSET at BASE.  Return 1 if we succeeded at
 167    mapping the data at BASE, -1 if we couldn't.
 168
 169    It's not possibly to reliably mmap a file using MAP_PRIVATE to
 170    a specific START address on either hpux or linux.  First we see
 171    if mmap with MAP_PRIVATE works.  If it does, we are off to the
 172    races.  If it doesn't, we try an anonymous private mmap since the
 173    kernel is more likely to honor the BASE address in anonymous maps.
 174    We then copy the data to the anonymous private map.  This assumes
 175    of course that we don't need to change the data in the PCH file
 176    after it is created.
 177
 178    This approach obviously causes a performance penalty but there is
 179    little else we can do given the current PCH implementation.  */
 180
 181 static int
 182 linux_gt_pch_use_address (void *base, size_t size, int fd, size_t offset)
 183 {
 184   void *addr;
 185
 186   /* We're called with size == 0 if we're not planning to load a PCH
 187      file at all.  This allows the hook to free any static space that
 188      we might have allocated at link time.  */
 189   if (size == 0)
 190     return -1;
 191
 192   /* Try to map the file with MAP_PRIVATE.  */
 193   addr = mmap (base, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, offset);
 194
 195   if (addr == base)
 196     return 1;
 197
 198   if (addr != (void *) MAP_FAILED)
 199     munmap (addr, size);
 200
 201   /* Try to make an anonymous private mmap at the desired location.  */
 202   addr = mmap (base, size, PROT_READ | PROT_WRITE,
 203                MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 204
 205   if (addr != base)
 206     {
 207       if (addr != (void *) MAP_FAILED)
 208         munmap (addr, size);
 209       return -1;
 210     }
 211
 212   if (lseek (fd, offset, SEEK_SET) == (off_t)-1)
 213     return -1;
 214
 215   while (size)
 216     {
 217       ssize_t nbytes;
 218
 219       nbytes = read (fd, base, MIN (size, (size_t)-1 >> 1));
 220       if (nbytes <= 0)
 221         return -1;
 222       base = (char *) base + nbytes;
 223       size -= nbytes;
 224     }
 225
 226   return 1;
 227 }
 228
 229 \f
 230 const struct host_hooks host_hooks = HOST_HOOKS_INITIALIZER;